In the manufacture of articles in a plastic injection molding process, it is necessary to strip molded articles from a mold core. One manner of stripping the articles is with a stripper plate associated with the mold core.
FIG. 1 is a front elevation illustrating a typical prior art stripper plate arrangement in the context of a multi-level molding apparatus generally indicated by reference 10. The apparatus 10 includes mold core support plates 12 and mold cavity support plates 14, mounted respectively to which are mold cores 16 and mold cavities 18. One of the mold core support plates is secured to a fixed platen 13 and the other is secured to a movable platen 15, the latter being carried by tie bars 20. The mold cavity support plates 14 are secured to a center manifold support plate 17.
A stripper plate 22 is associated with each mold core 16. The stripper plate 22 lies against the mold core 16 when the mold is closed and moves away from the mold core 16, as the mold approaches its fully open position. Movement of the stripper plate 22 away from the mold core 16 is caused by a lever arm 24 pivotably secured to the mold core support plates 12 by a connector 26. The lever arm 24 has a first leg 28 with a cam surface 30 which contacts a roller 32 serving as an actuator to cause clockwise rotation of the lever arm 24 about the connector 26 when the mold core 16 and mold cavity 18 reach a degree of separation determined by the location and profile of the cam surface 30. This causes a second leg 34 of the lever arm 24 to press against the stripper plate 22 to move the stripper plate 22 away from its associated mold core 16 to dislodge a molded article. The mold core support plates 14 are mounted on a center manifold plate support 17 which is also carried by the lowermost of the tie bars 20.
For simplicity, the operation of only one lever arm 24 is fully described above and illustrated in FIG. 1. In practice, at least one lever arm 24 would be associated with each mold level such as shown in dashed lines in FIG. 1. Furthermore, more than one lever arm 24 may be utilized at each mold level to balance the force being applied to the stripper plate 22.
In the prior art, the actuators or rollers 32 have been mounted directly on the mold cavity support plate 14. Such mounting has proven problematic, particularly in applications where deep parts are to be formed requiring considerable separation distances between the mold cores 16 and mold cavities 18 for stripping. In the prior art arrangement, large separation distances require very long first legs 28 on the lever arms 24 which reduces both rigidity and the amount of stripper platen movement for a given lever arm movement. Flex in the lever arms 24 caused by the use of long arms results in cocking of the stripper plate 22 further resulting in galling and jamming. Also, the first legs 28 of the lever arms 24 of adjacent mold levels have been positioned one behind the other to allow for overlap when the mold assembly is closed. The space required for overlap can cause interference with certain types of mold opening and closing linkage, such as, for example, the linkage arm arrangement illustrated in U.S. Pat. No. 5,707,666 (DiSimone et al.).
It is an object of the present invention to provide a stripper platen actuating arrangement which enables the use of considerably shorter lever arms than in the prior art arrangement described above.
It is a further object of the present invention to provide a stripper mechanism actuating arrangement which avoids interference with the mold opening and closing linkage.